web services that cannot be run with the current selection/data should not be presented to user

Currently, no tests are performed on the currrent selection or alignment frame before displaying calculation entries in the web services menu. In 2.5, a user can try to launch a multiple alignment a single sequence - and the result is a WS window containing the text 'Job never ran, input returned to user'.

Desirable behaviour:

 * if the job is not valid for the current selection/environment, the service entry should be greyed out, with some helpful tooltip text indicating why it can't be run.